Orbicularis oris muscle

The orbicularis oris ( " circular muscle of the mouth " ) is an annular sphincter around the mouth opening and forms the basis of the fleshy lips.

The tonic contraction of the orbicularis oris ensures the closing of the mouth opening. If the lips are contract only the outer portions tipped like to kiss ( in English it is often called the "kissing muscle" ).

The muscle is innervated by the seventh cranial nerve, the facial nerve (VII). A one-sided facial paralysis resulting in a drooping corner of the mouth and thus to leakage of saliva. The functioning of the nerve can be tested with the orbicularis oris - reflex. The blood supply is via the arteria labialis inferior and superior labial artery, both of which arise from the facial artery.